1. Field of the Invention
The present invention relates to a de-interlacing device and associated method, more particularly, a de-interlacing device capable of de-interlacing a video field adaptively and associated method.
2. Description of the Prior Art
When television is presented to the public, the technology of updating frequency at 60 times per second and writing at 525 lines (this is the National Television Standard Committee, a.k.a., NTSC) or updating frequency at 50 times per second and writing at 625 lines (this is the Phase Alternating Line, a.k.a., PAL) remains costly. Even scan lines and odd scan lines are transmitted each time alternatively, which is known as interlace. In the case of NTSC or PAL, the result is either, respectively, 30 or 25 frames being shown per second. The reduced frame rate reduces the hardware complexity while the overall bandwidth requirement is reduced because of the interlacing. The display fluency of the interlaced picture is still acceptable to the human eye.
Later personal computers were presented to the public. The monitor technology utilized by the personal computer is known as progressive scan. Liquid crystal display (LCD) and plasma display are only capable of displaying progressive scan images. If an interlace image is inputted into an LCD or plasma display then de-interlacing technology is thus needed.
FIG. 1 illustrates a functional block diagram of a conventional de-interlacing device 10. The de-interlacing device 10 comprises a de-interlacing unit 12 and a motion detector 14. The motion detector 14 detects a motion difference between a video field Field (n) and a plurality of video fields temporarily neighboring the video field, such as, Field (n−2), Field (n−1), and Field (n+1). The motion detector 14 outputs a motion ratio MR. The motion ratio MR corresponds to the motion ratio function of FIG. 2. The de-interlacing unit 12 performs de-interlacing according to the motion ratio MR and the neighboring video fields of Field (n).
The conventional motion detector 14 outputs a motion ratio MR according to a single motion ratio function regardless of the properties of the video field Field (n). For example, given this single motion ratio function, the image motion difference of a man dressed in black at night is insignificant; it can easily be incorrectly interpreted as a static picture. In another example, if a high motion ratio function is selected then motion change is easily spotted; however, black letterings on a white board will appear to be shaking or showing unstable flashes.